Clarification of Wiring AC Condenser


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Old 07-10-05, 08:43 AM
djc621
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Question Clarification of Wiring AC Condenser

Good morning!

I need to clarify replacing the existing wiring from the panel to the disconnect. I am going from a 30 amp circuit to a 45 (max breaker for 33.1 ampacity on the name plate). I will be changing the breaker to a 50 abl 2 pole.

Running new wire is not easy -must go through a ceiling and up to roof with no attic or crawl space so it must be pulled through exisiting conduit. I don't want to do it more than once! So, the existing conduit contains:

1 Red # 10
1 Black # 10
2 Black # 14

I was advised to pull 2 # 8 THHN black and 1 #12 green for ground.

The questions I have are:
1. What are the existing Black # 14 for? Are they the low volatage for the thermostat?

2. Should I leave them in the conduit. The AC instatller said I needed to have 2 hot and 2 cold (for 2 stage hot & cold thermostat).

3. Does that mean I have to add 2 more # 14 or can the exisiting # 14s be split?

I sincerely appreciate your advice and suggestions. Thanks!
 
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Old 07-10-05, 09:39 AM
Bob33
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Not sure about the wires but why are you using (if I understood) a 50 amp circuit breaker for a 35 amp max load? this will not protect the unit.
 
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Old 07-10-05, 10:41 AM
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You dont say for sure just what you have there that you have to work on. Is this inside blower coil outside condenser, heat pump or what. For the tstat wire to the unit you should need just 3 # 18 or 20 gauge

ED
 
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Old 07-10-05, 12:37 PM
djc621
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More info

Thanks for the reply. First, according to the name plate, the max fuse or breaker is 45 . I was told to use a 50 amp 2 pole in the breaker panel.

Second, the thermostat will control the forced air gas furnance and the A/C. I was told that I need 2 hot and 2 cold wires to run from the disconnect to the inside for the thermostat.

Does that make more sense? The question is whether the 2 #14 wires that are already in the conduit sufficient for the thermostat or if it is overkill, what should I pull at the same time as the 2 Black #8 and 1 #12 Greeen ground to the disconnect?

Thanks for your help.
 
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Old 07-10-05, 01:53 PM
ally68
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If it says max 45 why would you use 50amp? I would use 40 with a load of 33.
 
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Old 07-10-05, 02:11 PM
djc621
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Still Confused!

I was originally told to to get a 60 amp breaker, then the 50 2 pole. If the name plate says max breaker 45 and min circuit ampacity of 33.1. If I go with a 40 won't it trip very easily? Thanks for your reply!
 
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Old 07-10-05, 02:27 PM
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First...post everything that is listed exactly as it appears on the name plate. From what you have posted you cannot go over 45 amp HACR double pole breaker, there should be a minimum listed also. Your MCA is 33.1 so the minimum ampacity conducter must be at least #8 copper.
You appear to have a 2H 2C heat pump ie 2 stage heating and cooling. My experience has been if you dont incorporate an outside thermostat then you need five wires from furnace to heat pump 6 if you use an OT. I have no idea what 2 #14 wires would be needed for, typically #18 awg contol circuit wires are used. You purchase this wire as a cable with enough pairs to use for your application, any extra wires are just unused and capped off. They normally wire nut to the thermostat wires at the control module in the furnace.
 
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Old 07-10-05, 03:30 PM
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Originally Posted by djc621
I was told.....
You have been told some very different and erroneous information. "Who" is telling you all this???

I agree with Roger. Post exactly what this unit is and what it is connected to.

If it is a smiple A/C condensor then it needs a two wire low-voltage connection to the air handler. This is usually run with the copper line set since they follow the exact same path. Possibly this was not done so they ran conductors with the power feed.
The only way to tell is to tell us where they go and what they are connected to. Just saying two #14 in the conduit could be many different things.
My suspicion is that they are the t-stat wires since they are both black.

I also agree, why would you install a 50 or 60 if the unit clearly states 45 MAXIMUM.


Please post back with more info.
 
  #9  
Old 07-10-05, 04:22 PM
ally68
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The point of the breaker is to trip with overcurrent so if it is 33 you want to be as close to it as possible with out nusanse tripping and 7 amps over is alot with a 50 amp it would have to be 17 amps over that is quite alot.
 
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Old 07-10-05, 06:11 PM
djc621
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Name plate details

Thanks guys for your feedback. I really want to be clear before pulling the new wire.

I am replacing my AC condenser (on my roof), going from a 30 AMP to a 45 AMP. Here is the name plate data: 60 Hz, 1Phase, 197 Min Volatage. Max Fuse or Breaker -45. Min Ckt Ampacity 33.1. This unit is a 5 ton condenser and I was told I need two hot (furnace) and two cold (A/C) to go to the air handler and for thermostat. There are two #14 black wire in the exisitng conduit from the panel to the disconnect. The question was whether I should leve these in the conduit or replace them as I run the new 2 new #8s and 1 #12 green (ground) from the panel to the disconnect.

I've had two different suggestions for wiring (8 and 6) and two suggestions for breakers - 60 and 45. It seems to me that the breaker should be 45 per the plate. Thanks again!
 
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Old 07-10-05, 06:39 PM
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How long will the wire be from the main panel to the AC unit ?
Do you have a service disconnect located at the AC unit ?
 
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Old 07-10-05, 06:42 PM
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Ok, first, this is a heat pump assume, not a condensor?

If these two #14's are being used and are OK, leave them. Where are the other two wires you need? Are they in place or do you need to run them?

You also need to run a #10 ground for this circuit, not #12.
If the rating plate says *max* 45 amps, that is just that, the maximum. They do not make a 45 amp breaker so the next step down is appropriate, a 40. DO NOT go higher. #8cu is the correct wire.

I'll ask again, who is giving you this advice?
 
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Old 07-10-05, 07:01 PM
djc621
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AC Condenser

Hi guys,
Thanks for all your help so far.

This is strictly a condenser, not a heat pump. The air handler is a gas furnace (single stage). The distance from the breaker panel to the disconnect box is approximately 35 feet. Up 5 feet from the panel accross 25 feet of ceiling and up to the roof. I was told to use a 45 amp fused disconnect. The disconnect box is located about two feet from the condenser. The air handler/furnace is another 25 feet away. I will as you suggested run the thermostat wire along with the copper refrigerant and suction lines to the theremostat.

I still could use a definitive answer on the breaker size in the panel and your suggestion as to the wires (2 # 8 and 1 #12 ground ?) from the breaker panel to the disconnect.
 

Last edited by djc621; 07-10-05 at 07:02 PM. Reason: Correction #12 ground
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Old 07-10-05, 07:04 PM
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Post deleted to prevent confusion.
 

Last edited by Roger; 07-10-05 at 10:04 PM.
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Old 07-10-05, 07:19 PM
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I still could use a definitive answer on the breaker size in the panel and your suggestion as to the wires (2 # 8 and 1 #12 ground ?) from the breaker panel to the disconnect
I see the run is only 35 feet #8 THHN copper should be fine. You can go larger if you want.
You need a #10 EGC (ground)
Make sure the breaker is HACR rated. I would use a 40 as Speedy suggested. I believe they do make a 45 (though uncommon) so you could up to that if the compressor wont start with a 40.

If you only have 1 stage heating then you do not have 2 stage heating and cooling. You might have two stage cooling and 1 stage heating. I suggest you take a close look at you literature for this unit. Might be prudent to post down on the a/c and heat pump forum for these answers.
 

Last edited by Roger; 07-10-05 at 08:15 PM.
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Old 07-10-05, 08:02 PM
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Min Ckt Ampacity 33.1. This unit is a 5 ton condenser
I dont know of any 5 ton unit out to day that you dont put a 60 amp breaker on it Trane and Rheem both have a ampacity of 36 and call for a 60 amp breaker on it
By my book a 5 ton gets a 60 amp a 4 ton a 50 amp a 3 1/2 ton a 40 to 45 amp.

ED
 
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Old 07-10-05, 09:03 PM
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Yep, that has had me somewhat concerned also. My original thought was 45 would be the minimum and he must be mistaken. But he has stated three or more times that the nameplate states 45 amp max. What is your thoughts that this might be a scroll compressor unit? My understanding is that a scroll substantially decreases locked rotor and rated load current.


EDIT: I just looked at Rheem and all their units are scroll compressors. Their five ton unit takes a 60 amp max.breaker. I wonder what we have going on here?
 
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Old 07-10-05, 09:14 PM
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Originally Posted by djc621
I still could use a definitive answer on the breaker size in the panel and your suggestion as to the wires (2 # 8 and 1 #12 ground ?) from the breaker panel to the disconnect.
See the post right before the one quoted. I answered this clearly:

"You also need to run a #10 ground for this circuit, not #12.
If the rating plate says *max* 45 amps, that is just that, the maximum. They do not make a 45 amp breaker so the next step down is appropriate, a 40. DO NOT go higher. #8cu is the correct wire."



If this is a condensor you DO NOT need any control wires other than the pair between the AH and condensor. Why would an air conditioning condensor need control wires to a heating furnace???

I'll repeat it again. You are getting bad advice from who ever it is you are talking to.
I hope you get this all cleared up before you do any work. I would confirm any advice you are getting from any non-professionals. Advice from a friend who "has done some work" is a dangerous thing.
 
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Old 07-10-05, 09:31 PM
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Speedy I didnt mean to be redundant in your reply but he seemed to have missed your verifications of what he asked. I should have just pointed him back to your post. No you would not need control wires (should be saying low voltage wires) if this is a a/c condensor other than the two. I posted shortly after he stated it wasnt a heat pump. I just didnt go back and edit that out. My use of "control wires" was misleading my mistake, its the industrial part of me blocking my common sense The #14 wires is odd but I guess that doesnt matter I have thought from the beginning that these were the two wires for an a/c condensor.
 

Last edited by Roger; 07-10-05 at 10:11 PM.
  #20  
Old 07-11-05, 04:36 AM
djc621
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Thanks very much

Thanks very much to all of you. I will use a 40 breaker, #8 and #10 ground. To further clarify this is an Amana condenser with a scroll compressor that uses 410A. I sincerely appreciate all your help. I will not do the connections, someone with more experience will. I will just be pulling the wire so needed to be clear so as not to have to re-do it. Thanks again for everything.
 
  #21  
Old 07-11-05, 06:39 AM
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Ok it appears that Amana does make a residential 5-Ton Model#RSG60C2C that is 56,000 BTU that has a nameplate max. circuit breaker of 45 amps.
http://www.amana-hac.com/consumer/ch...stedSite=Amana
 
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Old 07-11-05, 12:21 PM
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I advised DJC to use #8 THHN B-C conductors, a 2-pole 50 amp C-B, and a #12 EGC ( if needed). The EGC should be #10, as corrected by others.

As the the 45/50 amp rating of the C-B, the minimum circuit ampacity for the conductors was specified as "33". This value is 125% of the full-load current (FLC) so we calculated the FLC as 27 amps. (approx).

Art. 440.22 (A) permitts a C-B rating not exceeding 175% of (1), the FLC, 27 amps or (2) the "branch-current selection current" (33 amps), whichever is greater.I interpret that the ampacity is "selected" by the 125% X FLC requirement.

(1) gives a value of 47 amps and (2) gives a value of 57 amps.

Art. 240.4 (B) , "Over-current protection" allows "rounding up" when the ampacity (47) is "between" standard ratings.

Also, Art 440.22 (A) states "where not sufficient for the starting current, the rating may be ( 225% of the FLC)."
 
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Old 07-11-05, 12:29 PM
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Model#RSG60C2C that is 56,000 BTU that has a nameplate max. circuit breaker of 45 amps.
Dont see how you can call that a 5 ton AC it takes 60,000 BTU to make 5 ton

 
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Old 07-11-05, 12:41 PM
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PATTBAA,

While all this is true, the fact of the matter is the units specifically states a MAXIMUM ocpd of 45 amps. We cannot round this number up.
That cannot be superseded by any other code.
 
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Old 07-11-05, 01:19 PM
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Originally Posted by Ed Imeduc
Dont see how you can call that a 5 ton AC it takes 60,000 BTU to make 5 ton

Yep cant argue that so guess technically it is a 4.67 ton . Maybe the use the HVAC round up rule
Seems the model # designates how they sell the thing ie RSG36(3 ton),RSG48(4 ton)and RSG60(5 ton) it really isnt but bet the salesmen say it is.


Dont panic DJC621 this is pretty normal
 
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Old 07-11-05, 01:39 PM
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Condenser

Thanks guys,

4.67 tons will be fine -once I get it installed. It's hotter than blazes right now-I'm still waiting for the conndenser to show up-they originally shipped the wrong one. This unit is rated as one of the 5 most efficient by the Feds and uses 410A, so at least it should last for a while-hopefully-cause I'm not doing this again.

Best regards,

DJC
 
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Old 07-11-05, 02:38 PM
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PATTBA

Not trying to get down on you or anything but this seems to be a good opportunity to show how I see a lot of people mis-using the code.

Remember that we have to use the whole code book and the entire pertinent articles for any given installation. Just skipping through parts of an article doesn't cut the mustard.

Look at 440.21

Article 440

III. Branch-Circuit Short-Circuit and Ground-Fault Protection

440.21 General.


The provisions of Part III specify devices intended to protect the branch-circuit conductors, control apparatus, and motors in circuits supplying hermetic refrigerant motor-compressors against overcurrent due to short circuits and grounds. They are in addition to or amendatory of the provisions of Article 240.


Also look at 440.22(C)

(C) Protective Device Rating Not to Exceed the Manufacturer’s Values. Where maximum protective device ratings shown on a manufacturer’s overload relay table for use with a motor controller are less than the rating or setting selected in accordance with 440.22(A) and (B), the protective device rating shall not exceed the manufacturer’s values marked on the equipment.

Just tryin to help here
 
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Old 07-11-05, 02:56 PM
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I think you will find that Trane XL19i AC unit will give you a seer of 19.50 for tops and that unit is still a R 22. That will be made till 2030 R 410a just cost to much if you have a leak at all.


ED
 
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Old 07-11-05, 02:59 PM
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Speedy...

His Post # 13 states. That he will install a 45 amp fused service disconnect at the AC unit.
This will cover the AC units specifications.

With this said can the run from the main panel to the fused service disconnect be a 50 amp breaker 2 # 6 wires and #10 ground ????
Then # 8 wire from the disconnect to the AC unit.
===========================

Djc621.

BTW,
If the existing conduit is 1/2" you will need to change it.
If you need control lines, Don't use the same conduit to feed low voltage control wires thru.
If something shorts out it can energize the low voltage wires and anything connected to them and start a fire.

" The air handler/furnace is another 25 feet away "
How are you going to power it ?
Thru the same conduit ?
 
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Old 07-11-05, 03:01 PM
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"That cannot be superceded by any other code ( including the NEC) " --- ( my addition)

I will cite the relevant Code Article in it's entirety-----

Art 440.22 Application and Selection ( Branch-Circuit Protection)

(A) Rating ( in amps) for Individual ( single) motor-compressor.

"The motor-compressor branch-circuit short-circuit ( or Ground-fault) protective device ( circuit-breaker) shall be capable of carrying the starting current of the motor.A protective device having a rating not exceeding 175% of the motor-compressor rated-load current, or Branch-Circuit selection-current, whichever is greater, shall be permitted ,provided that, where the protection specified is not sufficient for the starting-current of the motor, the rating shall be permitted to be increased but shall not exceed 225% of the motor rated load-current, or Branch-circuit selection-current, whichever is greater."

No restrictions or exceptions on the application of this Article appear in the Code.

As to the mimimum circuit ampacity, in this instance "33", Art 440.6, Ampacity, (A) motor-compressor, Exception 1 reads---- " where so marked , the Branch-Circuit selection current shall be used instead of the rated load-current to determine the rating of the Branch-Circuit protection."

I suspect that the "marked" value of "33" amps as the "minimum" conductor ampacity is based on the rated load-current X 125% = 33 amps,which is the "selected" current. A rated load-current of 33 X 175% would require a 60-amp breaker.

"
 
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Old 07-11-05, 03:42 PM
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"OVERLOAD relay table for use with a MOTOR CONTROLLER---"

It is important to distinguish , as applied to motors ,between OVER-CURRENT and OVER-LOAD protective devices. Over-current, or short-circuit and ground-fault protection of circuit-conductors, is completely different than Over-load protection which limits motor-current to a safe value.There are seperate sections in Art 430----Part lll, Over-load protection, and Part IV, conductor over-current protection.

A breaker in a motor-circuit has a larger rating than the conductors because it only protects against grounds and-short-circuits in the conductors, and does not included over-load protection.

"Over-load" , Art 100, "Definitions"----"operation in excess of (rated currents ). A fault, such as a short-circuit or ground-fault, is not an over-load"
 
  #32  
Old 07-11-05, 10:08 PM
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My understanding...Minimum Circuit Ampacity = (RLA x 1.25) + other loads
or (RLA x 1.25) + fan motor FLA(nameplate)


Max. overcurrent device = (RLA x 2.25) + (fan motor FLA) If this does not fall on a standard breaker size down to next standard breaker. UL para. 36.16 "standards for manufacturer HVAC nameplate ratings". Part of UL 1995 governing all hvac equipment.(see NEC110-3(b)

Branch Circuit Selection Current: (Overrides NEC Articles 440-2 and 440-4)
This is a manufacturers selection current that must be used in place of nameplate RLA in the calculation of branch circuit conductors, max. ocpd, disconnects and controllers. It will always be equal to or greater than the nameplate RLA. This value shall be listed whenever the running overload protective device allows a sustained current greater than the nameplate RLA.

Ok....I'm no expert at HVAC calculations and how they derive all these figures on the nameplates. I'm certainly better at it after this thread

My understanding is that you cannot exceed the nameplate MAX ocpd....unless...approved by a NEC engineeer in cases of deration and ambient temperatures. UL1995

It seems that we are unable to come up with 45 amps Max OCPD using the calculations listed in all these posts. Dont know if mine make a difference or not. Only things I see different is the next size down rule and other loads from previous posts. I havent ran any figures through them. But seems things wont change much unless we can get the actual FLA of the fan motor and rla of compressor and they would need to be considerably different tha what has been discussed so far.

Next size down rule would take a 57 amp for Max. OCPD calculation back to 50 amps not up to 60. A 47 amp calculation would go down to 45 MAX OCPD not 50.

At any rate I have a headache from all this....hope this information will reveal a solution to this disagreement we are having under friendly terms.

Some of this information I resourced off the net to give another aspect other than 2002 NEC. These were the articles I referenced...

http://www.iaei.org/magazine/00_d/johnston.htm

http://www.iaei.org/magazine/99_d/simmons.htm
 

Last edited by Roger; 07-11-05 at 10:37 PM.
 

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